Cannot login on AdminCP

Don't know if i'm here at the right place or need to create a ticket at vbulletin.com.

In January the server my forum is installed on ends PHP 5.6 and is only running PHP 7.2
There is already a possibility to test if the website (the forum) is working on PHP 7.2.
It does. As far as I can see it works well, exept the admincp.